Abstract Although medication assisted therapy (MAT) for opioid use disorders (OUD) is safe and effective and is currently considered the gold standard for treating OUD, adherence to MAT regimens remains a challenge. Initial studies have demonstrated efficacy of mindfulness-based interventions as adjunctive treatment for substance use disorders (SUD) while reducing substance use and cravings. Additionally, non-randomized pilot studies suggest that mindfulness-based interventions may be effective in reducing symptoms of depression and anxiety in individuals undergoing MAT for OUD.5 In addition, peer recovery support services delivered by individuals in recovery from SUD have also been found to be effective in reducing relapse rates, increasing treatment retention, and improving relationships with treatment providers and social supports.6 Nonetheless, recent studies that have used a combination of therapy and MAT have yielded mixed results, thereby necessitating further exploration.7-8 Several factors, including depression, anxiety, stress, and cravings affect adherence to MAT and other SUD treatment regimens because they increase likelihood of relapse.9-12 Additionally, physiologic stress reactivity and drug cue reactivity, often measured by the hormone cortisol have been shown to be predictors of relapse. The goal of the present study is to determine the effectiveness of a mindfulness-based intervention that also utilizes peer mentors in addition to professional substance abuse therapists (the Minds and Mentors program [MiMP]) in improving adherence to MAT for OUD and reducing relapse rates in a sample of individuals with OUD who are also on MAT versus a twelve-step facilitation (TSF) program. The MiMP is an eight-week intervention that uses group therapy and meets once a week for about two hours. We hypothesize that participants in MiMP will demonstrate better adherence, reduced relapse and cravings (primary outcomes measures), reduced depression, anxiety, and stress, and improved social support (secondary outcomes measures), and reduced cortisol levels and reactivity to drug cues (exploratory outcome measures). This study will utilize an individually randomized group treatment design. Data collection will occur at baseline (T0), end of treatment (T1), and at 3 (T2), 6 (T3), and 12 (T4) months follow-up. The findings of the study have the potential to impact policy and practice changes related to treatment of UUD and strategies to improve adherence to MAT. This intervention has the potential to ultimately decrease morbidity and mortality in individuals with OUD by decreasing relapse and other comorbid psychosocial outcomes such as depression, anxiety, and stress. Furthermore, this study may help in the identification of individuals who are more reactive to stress, and who may need treatments that incorporate additional elements focused on stress reduction.